Use Build Kit docker feature to shrink the Docker image size

[nicknezis]

Resolves #3666

The heron-install.sh file was being left in a Docker layer after the install. This is causing the Heron distribution image to be about 2.3 GB in size. This change helps drop the dize to roughly 1.1 GB.

[Code0x58]

Requiring docker buildx for builds sounds reasonable to me as people may usually have it from their reasonably up to date docker installation.

I tried to test the build process with the command below but it highlighted that debian9 doesn't have the required version of python, but the others built normally.

./scripts/release/docker-images "$(git describe --tags)" --all

It looks like there's ~190M of additional space which could be cut out of the heron install due to file duplication. I made #3670 for that in case anyone feels it's worth picking up.

[joshfischer1108]

Do we need to make any changes to the documentation to account for buildx?

[nicknezis]

Do we need to make any changes to the documentation to account for buildx?

That's a good question. I did a recursive grep through the repo for docker build. I think we either don't have enough documentation or it's referencing the bash scripts. I'll do a scan to look for other things that should be updated. Probably a good idea to mention the docker minimum version. I can update the version check script also.